In processing photographic films, especially black and white films, it is highly advantageous to complete the processing in a very short period of time. To accomplish this objective, it is common practice to process such films using a roller transport processor and to carry out the processing without an intervening washing step between the steps of developing and fixing. This method of processing is described, for example, in U.S. Pat. No. 3,545,971. To facilitate the use of a roller transport processor, both the developer and the fixer typically contain a hardening agent, with the hardening agent usually being an aldehyde in the developer and an aluminum salt in the fixer. Boric acid is often incorporated in the fixer used in the aforesaid process to prevent the formation of sludge resulting from precipitation of aluminum hydroxide when the fixer is contaminated by developer carry-in. Such use of boric acid is describe, for example, in U.S. Pat. No. 4,046,570.
To further promote the objective of a very short total processing time, it is advantageous to employ ammonium thiosulfate as the fixing agent, because it acts more rapidly than alternative fixing agents such as sodium thiosulfate, as described in GB 1,290,026. Additionally, the fixer contains a sulfite salt to stabilize the thiosulfate against decomposition with respect to time and temperature. Thus, a particularly desirable fixer is one which contains ammonium thiosulfate and a sulfite salt. The pH of these fixer baths is normally around 4.00-4.30, because at higher pH, especially more than 5.00, there is precipitation of Al(OH).sub.3. On the other hand, lower pH is correlated with high sulfur dioxide evolution, which is environmentally dangerous. Different solutions to the problem of reducing the sulfur dioxide evolution have been disclosed in the art.
Research Disclosure No. 15407, February 1977, discloses a method for reducing the evolution of sulfur dioxide from photographic fixing baths by adding a suitable quantity of a sulfite-complexing agent when preparing the working strength solution. This enables the sulfite concentration in the fixer concentrate to remain at the accepted high level required to stabilize the thiosulfate, but, upon dilution, the complexing agent will reduce the sulfate content to a sufficiently low level, that the evolution of sulfur dioxide is minimized. The sulfite-complexing agent may be an aldehyde, e.g., glutaraldehyde, ketone, e.g., acetone, or any compound which forms a relatively stable sulfite complex in aqueous solution in the pH range from 3 to 6.
Japanese Patent Application No. 05-119,445 describes a fixer for photographic materials containing specified amounts of ammonium thiosulfate and of sodium thiosulfate which do not generate toxic gases during processing.
Japanese Patent Application No. 04-019,739 describes a solid fixer for silver halide photographic material containing thiosulfate and sulfite and at least one of citric, tartaric, malic, succinic and phenyl acetic acids to prevent sulfur dioxide gas generation.
U.S. Pat. No. 5,298,382 describes a fixer concentrate containing a thiosulfate as a fixing agent, sulfite and water-soluble aluminum salt; the concentrated fixer is then diluted with water, thereby forming the working fixer solution containing a minimized amount of ammonium thiosulfate and of sodium thiosulfate, preventing the generation of sulfurous acid and ammonia gases.
In some cases the bad odors caused by the sulfur dioxide evolution has been reduced by adding specific compounds to the fixer, without reducing the sulfur dioxide evolution itself. In fact, Japanese Patent Application No. 05-313,320 describes a fixing liquid containing thiosulfate in concentrated state and diluted at time of use to prevent bad odors from being given off. In addition, a fixer composition comprising fixing agents, stabilizer, hardening agents and acids, e.g., succinic or maleic acid, has been disclosed in Japanese Patent Application No. 05-127,323.
European Patent Application 620,483 describes a method of image formation to reduce visible appearing disturbed lines observed at the surface of processed films. The method includes treating a silver halide material with a developer comprising at least one anionic alkylphenoxy polyalkyleneoxy phosphate ester surfactant and a fixer which may comprise at least one alpha-ketocarboxylic acid in an amount from 1 to 2 grams per liter, the material containing at least one polyoxyalkylene compound as a surfactant, a hardening agent different from vinyl sulphone and at least a non-sensitive protective antistress coating. The alpha-ketocarboxylic acid compounds therein disclosed are oxalic acid, glyoxilic acid and pyruvic acid compounds.
It could be useful to have a photographic fixer composition showing a reduced sulfur dioxide emission.